If this has been brought up before then I apologize. But I would like to hear from anyone who owns and/or has built a 6.8 AR on what the barrel thread pitch was, who made the barrel, and what you used for a flash hider. From what I understand the common thread pitch is supposed to be 5/8x24 TPI. The vortex flash hider made for 6.8 SPC rifles is threaded for this as well. But I just receieved my barrel from Model 1 sales and its threaded for 1/2x36 TPI, which is what RRA and Colt use on their 9mm rifles. I'm just curious as to who else has run into a similar situation.

My barrel is Made by E.R. Shaw. I don't know why they made it that way. Smith Enterprises lists a 6.8 Vortex with 5/8-24. Part # 1068V. I have contacted them to see if they can help me out. Or see if the 9mm one would work if it would even be any different.

Originally Posted By Cataclysm:My barrel is Made by E.R. Shaw. I don't know why they made it that way. Smith Enterprises lists a 6.8 Vortex with 5/8-24. Part # 1068V. I have contacted them to see if they can help me out. Or see if the 9mm one would work if it would even be any different.

Other makers like PRI have standardized on 5/8-24 which is also the standard for many 30 caliber rifles like the AR-10 and Remington 700.Lots of muzzle accessories available in 5/8-24, but most are big and heavy.You can use most 30 caliber suppressors with a 6.8.

You could certainly use Smith's 9mm vortex if it's 1/2-36, but it might not be as effective as a 30 caliber or 6.8 model.

I have some 30 caliber vortexes I got from Smith that are 9/16-24, but they are small like a 5.56 model, not huge like a 5/8-24 308 caliber version.If Smith is making a dedicated 6.8 vortex that's threaded 5/8-24 without the radial groove on it for a blank firing adapter and it's the size of a 5.56 model, that's the hot ticket.I just checked and they are not.Smith 6.8 VortexLooks to be 0.985" diameter, which is the same as the 308 version, big and heavy.The PDF file even mentions that it works on a 30 caliber weapon, so I bet it's just a re-labeled 30 caliber model.

The smaller 0.860" diameter 30 caliber 9/16-24 vortexes I have are pretty sweet.They match the AR-15 rifle better than the big 308 version, but you are stuck with a 9/16-24 thread which is less common.

I just talked to someone at Smith and it sounds like they have had a few inquires about the 1/2-36 threads. He took the words right out of my mouth before I could even tell him the thread pitch. I brought up the 9mm issue an he noted that they varied a little bit from the other models. I think it has to do with the shoulder dimensions or thread length, i'm not exactly positive. But either way it sounds like they will make some 6.8 flash hiders in 1/2-36.

He asked who made the barrel (for reference I assume) and I just told him it was made for M1S by E.R. Shaw. He also mentioned that a few AR builders seem to be comming up with their own threads instead of using more standard or common ones. I would imagine it would become very frustrating after a while.

however most barrel makers make the 5/8-24 threads too short for the standard 308 vortex, the back of the vortex must be modified. I personally like the 5/8 thread size on the 6.8, although I have seen 1/2-28 threaded barrels in 6.8, it looks flimsy without a muzzle devise.

Originally Posted By Toolman_556:however most barrel makers make the 5/8-24 threads too short for the standard 308 vortex, the back of the vortex must be modified. I personally like the 5/8 thread size on the 6.8, although I have seen 1/2-28 threaded barrels in 6.8, it looks flimsy without a muzzle devise.

Correct.The 308 Vortex is designed for the AR-10 which is standardized on a longer thread length than the AR-15 family.You are seeing 5/8-24 x 5/8" on AR-15's while the AR-10 is more like 5/8-24x3/4"I can thread to any spec, depending on what the muzzle device really needs.

1/2-28 on a 6.8 SPC barrel leaves the barrel wall 0.085" thick at the base of the threads.I have a simple chart about 2/3 of the way down my FAQ page that shows you barrel wall thicknesses at the base of the threads with different thread specs on different bore sizes.Very interesting indeed when you consider Colt threads 9mm barrels 1/2-36...